#include "postorderTraversal.h"
void postorderTraversal(TreeNode* root, vector<int>& cache)
{
    if (!root)
        return;
    else
    {
        postorderTraversal(root->left, cache);
        postorderTraversal(root->right, cache);
        cache.push_back(root->val);
    }
}
vector<int> postorderTraversal(TreeNode* root)
{
    vector<int> res;
    postorderTraversal(root, res);
    return res;
}